Fluid Domain Re-scaling
A fluid simulation uses a certain number of divisions to determine the resolution of the fluid. The number of divisions is related to the domain size in that 1 division will be 1/Domain Size blender units. Therefore scaling up the domain will make each division larger, so your fluid will be less smooth when you scale up the domain.

To make your fluid smoother, select your domain object and adjust the resolution values in the physics tab in the fluid settings. If you are looking for the exact same resolution as you had before, multiply the current resolution value by the amount you scaled the domain (if you scaled the domain by 2, multiply the resolution by 2, etc.). Blender allows you to do math equations in the input boxes as well so it should be fairly easy.